The invention relates to a method of consolidating an underground formation. In particular, the present invention relates to a method of consolidating those parts of an underground formation that surround a well or borehole penetrating the formation.
In one respect, the present invention relates to an improved procedure for consolidating an underground formation by the process described in the F. H. Meijs and D. R. Davies U.S. Pat. No. 4,061,191. That method relates to consolidating an unconsolidated gas reservoir by treating it to the extent required to ensure the presence of a significant but small amount of water absorbed on the rock surfaces then injecting enough gaseous silicon polyhalide to convert enough of that water to a grain-bonding silica gel to increase the competency without significantly reducing the permeability. The disclosures of the U.S. Pat. No. 4,061,191 patent are incorporated herein by cross reference.
As indicated in the U.S. Pat. No. 4,061,191 patent, numerous procedures have been proposed for utilizing liquid or gaseous silicon polyhalides in a treatment of subterranean reservoirs. For example, U.S. Pat. No. 2,019,908 discloses plugging a subterranean formation by injecting a nonaqueous silicon polyhalide and then allowing water to infuse and react. U.S. Pat. No. 2,469,354 teaches that a gas drive oil recovery process can be improved by injecting a gas which contains a halosilane and causes an oil-wetting of the rocks and/or plugging of a thief zone. U.S. Pat. No. 2,633,919 teaches that a reservoir can be oil-wetted by injecting a nonaqueous liquid containing a hydrocarbon-substituted silicon halide and then injecting water to hydrolyze the adsorbed halide. U.S. Pat. No. 2,808,886 teaches that a gas drive oil recovery process can be improved by including vapors of volatile hydrolyzable inorganic liquid and water in the gas to form permeability controlling or water-layer-plugging solid metal oxides or silica gels. U.S. Pat. No. 3,055,425 teaches that a reservoir can be consolidated and stabilized by injecting a nonaqueous liquid containing a silicon halide and then heating the treated zone to above about 300.degree. F. U.S. Pat. No. 3,055,426 teaches that where a formation to be consolidated with a silicon halide is oil-wet it should be pretreated with a surfactant which renders the formation water-wet. U.S. Pat. No. 3,087,542 teaches that a water-bearing formation can be plugged by injecting gaseous silicon tetrafluoride to finger through the water and form a radially extensive plug. U.S. Pat. No. 3,090,435 teaches that by injecting a wate-in-oil emulsion followed by a nonaqueous liquid containing a silicon halide, an unconsolidated reservoir can be consolidated. U.S. Pat. No. 3,221,505 teaches that a barrier plug can be formed by injecting a water-miscible liquid followed by a gaseous silicon tetrachloride to form a plug along the interface between it and the water. U.S. Pat. No. 3,252,513 teaches that water can be excluded from a well being gas drilled by injecting aqueous ammonia into a water producing carbonate reservoir ahead of an oil solution of silicon tetrachloride.
U.S. Patent application Ser. No. 117,697 filed Feb. 1, 1980, now Pat. No. 4,241,791 by D. R. Davies and E. A. Richardson also relates to an improvement in the U.S. Pat. No. 4,061,191 process; for increasing the uniformity of the consolidation of reservoirs containing layers of different effective permeability. In the process of that application the reservoir is pretreated by injecting a permeability-adjusting smoke so that substantially dry solid particles are screened out on the faces of the layers in a manner tending to equalize their effective permeabilities. In such reservoirs the present invention can be used in conjunction with the process of that application and the disclosures of the application are incorporated herein by cross-reference.
Underground formations containing fluids such as hydrocarbon fluids (oil and/or gas) or water that are being recovered via the wells penetrating such formations, often comprise layers of unconsolidated or incompletely consolidated formation grains. Such grains (hereinafter also referred to as sand or sand particles) may be torn from the formations by fluid flowing into the wells, and are likely to obstruct the fluid passages in the well and/or the surface equipment communicating with the well. The tubing in the well may even be locally damaged by the erosive action of sand carried by the fluid streams that impinge on the walls of the tubing.
Numerous techniques for consolidating such sand-producing formations have already been proposed in the past, and a number of these techniques have been proven successful in the field. The consolidating agents that are used in these techniques are of widely differing compositions, such as various types of resinous materials, water glass compositions, aluminum oxide cementing materials, and silicon halide compounds.
The present invention relates in particular to formation consolidating treatments using silicon halide compounds as the consolidating agents. These agents have been found to be easy to employ in the field. By a simple injection technique, the silicon halide compound can be injected either in gaseous or in liquid form down the well and into the formation parts to be treated. As indicated in the U.S. Pat. No. 4,016,191 patent, it is imperative that some water be present around the contact points of adjacent sand grains in the formation parts into which the silicon halogen compound is injected. The following reaction will then take place: EQU SiCl.sub.4 +2H.sub.2 O.fwdarw.SiO.sub.2 +4HCl,
and the amorphous silicon dioxide formed by this reaction will bond the formation grains together, thereby increasing the compressive strength of the formation parts. In order to retain a sufficient permeability of the consolidated formation parts, the water should be present in relatively small quantities.
The majority of underground formations that are to be treated for consolidation purposes are water-wet and can be consolidated by means of a silicon halide without a water-wetting pretreatment. In general, underground formations either already contain water adhering to the walls of the pore space, or can easily be wetted by injecting water thereinto via the well or borehole that penetrates the formation parts to be consolidated. When an excessive amount of water is present in the pore space of such a formation, this might lead to an undesirable reduction of permeability after the consolidation. In such situations, prior to injecting the consolidating agent, the excess amount of water should be displaced from the formation parts to be consolidated by injecting dry gas through the pore space (in case of a gas-containing formation) or injecting a non-polar liquid therethrough (in case of a liquid-containing formation). The volume of the water-displacing fluid is to be chosen such that a sufficient amount of water remains on the wall of the pore space for consolidating purposes without undesirable permeability impairment. As indicated in the U.S. Pat. No. 4,061,191 patent, the water content is preferably adjusted to from about 3- 7% by weight.
The application of silicon halide compounds as consolidating agent is in particular advantageous since it does not require a pretreatment of the formation whereby all the water is removed from the pore space of the formation parts to be treated, as is required in almost all other consolidating operations. In those other operations the presence of a water film on the surface of the formation particles prevents the consolidating agent from bonding to the surface of the formation particles, which results in a weak consolidation. Water removal from the surface of water-wet formation particles is a costly operation and in practice has been found to be difficult to carry out with the required efficiency, and it will be appreciated that it is found attractive to use a consolidating agent that reacts with water present around the contact points of adjacent sand grains. Such agent can be placed in the formation by means of a simple operation that can be carried out at relatively low cost.
Although the sand consolidation treatments described in the U.S. Pat. No. 4,016,191 patent have been generally successful, samples from certain reservoirs or certain portions of reservoirs have indicated a need for imparting a greater compressive strength. In those situations the reservoir rocks within the zone being treated were found to be only partially water-wetted. For example, in a typical sample of sand grains that were partially consolidated, it was found that although some portions of the grain surfaces were water-wet (and were bonded to a coating of siliceous cement) other portions were not water-wetable and were free of such a cement.